We proved in our experiments that the laser fading process removes efficiently indigo-dye from denim support. Different laser pulse parameters were used in order to obtain laser power density and fluence to start the ablation process. The purpose of this work is to determine the change of denim diffuse reflectivity spectra during laser irradiation with different wavelength and different power density. The change of diffuse reflectivity coefficient was up to 17% at 450 nm wavelength (from 8% reflectivity for unirradiated denim). We use the beams from Nd:YAG laser (1064 nm and its second harmonic 532 nm) and CO2 lasers.
We present experimental results of the Mueller matrix associated to GaAs on the (001) direction, with a Si concentration of 8 X 1017 cm-3. Laser light of 632.8 nm wavelength was used and there were taken measurements on the scattered light employing an scatterometer of the Angle-Resolved Scattering type and for an incidence angel of 10 degree(s).
Photoluminescence (PL) from (Al, Ga)As quantum-wire arrays grown on vicinal (111)B GaAs substrates by molecular beam epitaxy is reported for the first time. A peak at 1.826 eV is attributed to excitonic recombination in the built-in quantum-wire array, and a peak at 1.759 eV and a low PL emission band also originate from the serpentine superlattice structure. For comparison, the epilayers were also deposited on (100) GaAs substrates simultaneously. But the PL results indicate that they are the alloy-well structures. We explain these PL results with a model and draw a conclusion that steps on (111)B surface can play a very important role in crystal growth.
We report on experiments in which alkali metals were probed in (commercial) hollow-cathode discharge lamps, using simple semiconductor diode lasers. A variety of spectroscopic techniques have been employed to demonstrate the versatility of the set-up, including Doppler- limited absorption, fluorescence and optogalvanic spectroscopies, and Doppler-free polarization spectroscopy.
HeCd+ lasers based on hollow-cathode designs may be operated under conditions in which multi-line emission (white-light laser) can be realized. It has been shown that all laser lines attributed to transitions in Cd II are accompanied by contributions from the complex He(DOT)(DOT)Cd+ which also exhibit some gain. A diode laser probe has been used to investigate the line profiles of some of the laser transitions, and to explore the role of energy transfer in helium-cadmium collisions.
In optical storage technology, gratings consisting of curved grooves have been formed in disks to record data and in integrated optical pickup devices to read signal. Groove parameters, such as pitch, width, and depth, can be inspected by the light diftraction method. Diffraction patterns are usually analyzed without considering the curvature of grooves. A model is developed to examine diffraction patterns of curved grooves. Theories for uncurved and curved grooves are compared. An optical inspection system is developed. Experimental results are analyzed and compared with theories.
We describe both reflectance anisotropy and electroreflectance measurements carried out to
determine the physical origin of the anisotropies observed in the reflectance spectrum of (001) and
(110) GaAs. We find an anisotropy component which depends on impurity concentration for both
(001) and (110) surfaces [and on conductivity type for (001) GaAs]. This component is actually a
bulk-related electro-optic effect produced by the electric field present at the semiconductor surface.
This electric field is due to the pinning of the Fermi level at surface states. We find that a linear
electro-optic effect is responsible for the impurity-dependent aniso tropies observed in GaAs (001),
while a quadratic electro- optic effect is responsible for those observed in GaAs (110). We give an
estimate for the linear electro-optic coefficients of GaAs at energies around the E1 and E1 + z